Acrylonitrile-butadiene rubber general properties

Before reviewing in detail the fundamental aspects of elastomer blends, it would be appropriate to first review the basic principles of polymer science. Polymers fall into three basic classes plastics, fibers, and elastomers. Elastomers are generally unsaturated (though can be saturated as in the case of ethylene-propylene copolymers or polyisobutylene) and operate above their glass transition temperature (Tg). The International Institute of Synthetic Rubber Producers has prepared a list of abbreviations for all elastomers [3], For example, BR denotes polybutadiene, IRis synthetic polyisoprene, and NBR is acrylonitrile-butadiene rubber (Table 4.1). There are also several definitions that merit discussion. The glass transition temperature (Tg) defines the temperature at which an elastomer undergoes a transition from a rubbery to a glassy state at the molecular level. This transition is due to a cessation of molecular motion as temperature drops. An increase in the Tg, also known as the second-order transition temperature, leads to an increase in compound hysteretic properties, and in tires to an improvement in tire traction... 

The natural rubber does not generally exhibit all the desired properties for use in the rubber industry. Thus, it is possible to obtain better mechanical and physical properties at a lower cost by blending natural rubber with synthetic rubbers. Normally, natural rubber is deteriorated by ozone and thermal attacks due to its highly unsaturated backbone, and it also shows low oil and chemical resistances due to its non-polarity. However, these properties can be achieved by blending it with low unsaturated ethylene propylene diene monomer rubber, styrene butadiene rubber, carboxylate styrene butadiene rubber, nitrile butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene rubber, and acrylonitrile butadiene rubber. 

Many applications are being found for synthetic rubbers, which are synthetic polymers possessing rubber-like properties. Among those available commercially are butadiene-styrene and butadiene-acrylonitrile (called Buna rubbers), polyisoprene, and polybutadiene. Their properties may be modified considerably more than vulcanized rubbers, particularly with respect to resistance to oxidizing agents, solvents, and oils. Their adhesion to metals, however, is generally poorer. 

Aspects of viscosity, elasticity, and morphology have been discussed in general terms by various workers [73-76]. Rheological studies specific to particular polymers include dynamic rheological measurements and capillary rheometry of rubbers [77], capillary rheometry of PP [78], degradation of PP [79], torsion rheometry of PE [80], viscosity effects in blends of PC with styrene-acrylonitrile and acrylonitrile-butadiene-styrene [81], peel adhesion of rubber-based adhesives [82], and the effect of composition of melamine-formaldehyde resins on rheological properties [83]. 

Compatible Polyblends. When the polymeric materials are compatible in all ratios, and/or all are soluble in each other, they are generally termed polyalloys. Very few pairs of polymers are completely compatible. The best known example is the polyblend of polyCphenylene oxide) (poly-2,6-dimethyl-l,4-phenylene oxide) with high-impact polystyrene (41). which is sold under the trade name of Noryl. It is believed that the two polymers have essentially identical solubility parameters. Other examples include blends of amorphous polycaprolactone with poly(vinyl chloride) (PVC) and butadiene/acrylonitrile rubber with PVC the compatibility is a result of the "acid-base" interaction between the polar substituents (1 ). These compatible blends exhibit physical properties that are intermediate to those of the components. 

Whilst the peroxide-initiated emulsion polymerized polybutadiene had disappointing properties it was found in 1929 that copolymerization of butadiene with styrene and in 1930 with acrylonitrile led to the production of interesting materials. The butadiene-styrene rubber. Buna S, was potentially a general purpose rubber but at that time not competitive with natural rubber. On the other hand the butadiene-acrylonitrile rubber. Buna N, now commonly known as nitrile rubber had certain properties such as oil resistance not shown by natural rubber and commercial production was started about 1935. Commercial production of butadiene-styrene rubber did not commence until 1937 and many things were to happen before it became the world s most used rubber. 

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